Advanced handler wafer bonding and debonding

ABSTRACT

A method for processing a semiconductor wafer includes applying a release layer to a transparent handler. An adhesive layer, that is distinct from the release layer, is applied between a semiconductor wafer and the transparent handler having the release layer applied thereon. The semiconductor wafer is bonded to the transparent handler using the adhesive layer. The semiconductor wafer is processed while it is bonded to the transparent handler. The release layer is ablated by irradiating the release layer through the transparent handler with a laser. The semiconductor wafer is removed from the transparent handler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 13/649,458, filed Oct. 11, 2012, the entire contents of whichis incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to wafer debonding and, morespecifically, to advanced methods for handler wafer debonding.

DISCUSSION OF THE RELATED ART

Three-dimensional (3D) chip technologies include 3D integrated circuits(IC) and 3D packaging. 3D chip technologies are gaining widespreadimportance as they allow for greater integration of more complexcircuitry with shorter circuit paths allowing for faster performance andreduced energy consumption. In 3D ICs, multiple thin silicon waferlayers are stacked and interconnected vertically to create a singleintegrated circuit of the entire stack. In 3D packaging, multiplediscrete ICs are stacked, interconnected, and packaged together.

Modern techniques for 3D chip technologies, including both 3D ICs and 3Dpackaging, may utilize through-silicon vias (TSV). A TSV is a verticalinterconnect access (VIA) in which a connection passes entirely througha silicon wafer or die. By using TSVs, 3D ICs and 3D packaged ICs may bemore tightly integrated as edge wiring and interposer layers are notrequired.

Temporary wafer bonding/debonding is an important technology forimplementing TSVs and 3D silicon structures in general. Bonding is theact of attaching a silicon device wafer, which is to become a layer in a3D stack, to a substrate or handling wafer so that it can be processed,for example, with wiring, pads, and joining metallurgy, while allowingthe wafer to be thinned, for example, to expose the TSV metal of blindvias etched from the top surface.

Debonding is the act of removing the processed silicon device wafer fromthe substrate or handling wafer so that the processed silicon devicewafer may be added to a 3D stack.

Many existing approaches for temporary wafer bonding/debonding involvethe use of an adhesive layer placed directly between the silicon devicewafer and the handling wafer. When the processing of the silicon devicewafer is complete, the silicon device wafer may be released from thehandling wafer by various techniques such as by exposing the wafer pairto chemical solvents delivered by perforations in the handler, bymechanical peeling from an edge initiation point or by heating theadhesive so that it may loosen to the point where the silicon devicewafer may be removed by sheering.

3M has developed an approach which relies on light-to-heat-conversion(LTHC) whereby bonding is performed using an adhesive layer and a LTHClayer. Debonding is then performed by using an infrared laser to heat upthe LTHC layer and thereby loosening or “detackifying” the adhesive tothe point where the silicon device wafer may be removed. However, theLTHC layer is dark colored and highly opaque making it difficult toinspect the underlying circuitry prior to removing the silicon devicewafer from the handling wafer, which is generally transparent. Moreover,the LTHC approach employs a YAG laser operating at the infrared (IR)wavelength of 1064 nm, which while effective at generating heat in theLTHC layer and greatly diminishing the bonding strength of the adhesive,is not sufficient to fully and completely ablate the interface resultingin effectively zero adhesion.

SUMMARY

A method for processing a semiconductor wafer includes applying arelease layer to a transparent handler. An adhesive layer, that isdistinct from the release layer, is applied between a semiconductorwafer and the transparent handler having the release layer appliedthereon. The semiconductor wafer is bonded to the transparent handlerusing the adhesive layer. The semiconductor wafer is processed while itis bonded to the transparent handler. The release layer is ablated byirradiating the release layer through the transparent handler with alaser. The semiconductor wafer is removed from the transparent handler.

The release layer may be strongly absorbs a frequency of light radiatedfrom the laser. Light may be radiated from the laser is ultravioletlight. The light radiated from the laser may have a wavelength ofapproximately 350 to 360 nm. The laser used for ablating the releaselayer may be a YAG laser or a XeF excimer laser. The adhesive layer maybe applied to the semiconductor wafer. The release layer may be curedprior to bonding the semiconductor wafer to the transparent handler withthe release layer applied thereto. The adhesive layer may be applied tothe release layer. The release layer may be cured prior to applying theadhesive layer.

The laser used for ablating the release layer may be a diode-pumpedsolid-state (DPSS) laser. The laser used for ablating the release layermay be an excimer laser. The laser used for ablating the release layermay be a relatively low power laser compared to an excimer laser. Therelatively low power may be in the range from approximately 5 Watts to30 Watts. Processing the semiconductor wafer while it is bonded to thetransparent handler may include thinning the semiconductor wafer.Processing the semiconductor wafer while it is bonded to the transparenthandler may include creating one or more through-silicon via (TSV).

The method may additionally include inspecting the semiconductor waferthrough the transparent hander and the release layer after theprocessing of the semiconductor wafer and prior to ablating the releaselayer. Repairs may be performed on the semiconductor wafer prior toablating the release layer when the inspection reveals a correctabledefect. The semiconductor wafer may be added to a 3D stack afterremoving the semiconductor wafer from the transparent handler.

The release layer may be substantially transparent to visible light.

A method for processing a semiconductor wafer includes applying arelease layer strongly absorbent of ultraviolet light to a transparenthandler and substantially transparent to visible light. An adhesivelayer is applied between the release layer and a semiconductor wafer.The semiconductor wafer is bonded to the transparent handler using theadhesive layer. The semiconductor wafer is processed while it is bondedto the transparent handler. The release layer is ablated by irradiatingthe release layer through the transparent handler with ultravioletlight. The semiconductor wafer is removed from the transparent handler.

The method may additionally include inspecting the semiconductor waferthrough the transparent hander and the release layer after theprocessing of the semiconductor wafer and prior to ablating the releaselayer and performing repairs on the semiconductor wafer prior toablating the release layer when the inspection reveals a correctabledefect.

A bonded semiconductor wafer includes a transparent handler. A devicewafer is bonded to the transparent handler. A release layer, vulnerableto ablation by ultraviolet laser radiation and transparent to visiblelight, is provided directly on the transparent handler, between thetransparent handler and the device wafer. An adhesive layer isinterposed between the transparent handler and the device wafer.

The transparent handler may include Borofloat glass. The transparenthandler may be substantially transparent to ultraviolet and visiblelight. The transparent handler may be approximately 650 μm thick. Thedevice wafer may include integrated circuit elements. The device wafermay include one or more through-silicon via (TSV). The device wafer maybe a layer for a 3D integrated circuit or 3D package.

The adhesive layer may be TOK A0206. The release layer may include anadhesive. The release layer may include HD3007. The release layer mayinclude cyclohexanone. The release layer may be approximately 6 μmthick. The release layer may strongly absorbs a frequency of lightradiated from an ablating laser. The frequency of light radiated fromthe ablating laser may be approximately 350 to 360 nm.

The power of light radiated from the ablating laser may be approximately5 to 30 Watts.

The release layer may be vulnerable to ablation by ultraviolet laserradiation. The release layer may be vulnerable to ablation byultraviolet laser radiation of a power within the range of approximately5 to 30 Watts.

The transparent handler, the adhesive layer, and the release layer maybe configured to permit inspection of the device wafer therethrough.

A bonded semiconductor structure includes a transparent substrate. Asemiconductor wafer is bonded to the transparent substrate. A firstadhesive layer is interposed between the transparent substrate and thesemiconductor substrate. A second adhesive layer, vulnerable todestruction by ultraviolet laser radiation and transparent to visiblelight, is provided directly on the transparent substrate and between thesemiconductor wafer and the transparent substrate.

The second adhesive layer may include HD3007 or cyclohexanone.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present disclosure and many of theattendant aspects thereof will be readily obtained as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings, wherein:

FIG. 1 is a flow chart illustrating an approach for performing handlerwafer bonding and debonding in accordance with exemplary embodiments ofthe present invention;

FIG. 2 is a schematic diagram illustrating bonding and debonding of adevice wafer to a handler in accordance with exemplary embodiments ofthe present invention;

FIGS. 3A and 3B are schematic diagrams illustrating patterns of applyingthe laser light to a top surface of the handler in accordance withexemplary embodiments of the present invention; and

FIG. 4 is a schematic diagram illustrating a scanning laser debondingsystem in accordance with exemplary embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

In describing exemplary embodiments of the present disclosureillustrated in the drawings, specific terminology is employed for sakeof clarity. However, the present disclosure is not intended to belimited to the specific terminology so selected, and it is to beunderstood that each specific element includes all technical equivalentswhich operate in a similar manner.

Exemplary embodiments of the present invention provide variousapproaches for the temporary bonding and debonding of a silicon devicewafer to a handling wafer or other substrate that utilize an adhesivelayer and a distinct release layer. The release layer may be transparentso that the underlying circuitry of the silicon device wafer may beoptically inspected prior to debonding. Debonding may be performed byablating the release layer using a laser. The laser used may be anultraviolet (UV) laser, for example, a 355 nm laser. This wavelength isparticularly attractive due to the availability of robust and relativelyinexpensive diode-pumped solid-state (DPSS) lasers.

Because the bonding of the silicon device wafer to the handling waferincludes the use of both an adhesive layer and a distinct release layer,the bonding process may be referred to herein as hybrid bonding.According to one approach for hybrid bonding, the release layer may bean ultraviolet (UV) ablation layer and it may be applied to the handlingwafer, which may be a glass handler. The UV ablation layer may then becured. The bonding adhesive that forms the adhesive layer may then beapplied to either the glass handler or the silicon device wafer. The UVablation layer may include a material that is highly absorbing at thewavelength of the laser used in debonding. The material may also beoptically transparent in the visible spectrum to allow for inspection ofthe adhesive bonded interface. Both the UV ablation layer as well as thebonding adhesive are chemically and thermally stable so that they canfully withstand semiconductor processes including heated vacuumdepositions including PECVD and metal sputtering, thermal bake steps aswell as exposure to wet chemistries including solvents, acids and bases(at the edge bead regions of the bonded wafer interface).

An exemplary glass preparation process may begin with the UV ablationmaterial being applied e.g. by spin coating onto the glass handler. Theglass handler with UV ablation material spin-coated thereon may then besoft-baked to remove any solvent. Spin coating parameters may depend onthe viscosity of the UV ablation layer, but may fall in the range fromapproximately 500 rpm to approximately 3000 rpm. The soft-bake may fallin the range from approximately 80° C. to approximately 120° C. Thetemperature of the final cure may fall in the range from 200° C. to 400°C. Higher cure temperatures may be more effective at ensuring thermalstability of the UV ablation layer during standard CMOS BEOL processingwhich may take place between 350° C. and 400° C. For stronglyUV-absorbing or UV-sensitive materials, very thin final layers on theorder of approximately 1000 Å to approximately 2000 Å thick may besufficient to act as release layers. One such material is Shin Etsu ODL38 which may be spin applied to glass and cured in a nitrogenenvironment at 350° C. for approximately 1 hour to produce a film on theorder of 1000 Å thick. Such a film may be optically transparentthroughout the visible spectrum, but strongly sensitive to decompositionin the UV wavelength range below ˜360 nm, and may be fully and cleanlyablated using common UV laser sources such as an excimer laser operatingat 308 nm (e.g. XeCl) or 351 nm (e.g. XeF) or a diode-pumped tripled YAGlaser operating at 355 nm.

According to exemplary embodiments of the present invention, the bondingadhesive may be any temporary or permanent adhesive desired. The bondingadhesive may be applied to either the glass (e.g., after the UV ablationlayer is added) or to the device wafer. Because the UV ablation layercontrols the glass release, the adhesive may be chosen irrespective ofits UV absorption characteristics. This vastly increases the possiblechoices. For relatively low-temperature wafer applications (e.g. up to˜250° C.) a wide variety of materials exist (e.g. TOK TZNR-0136) whichcan be bonded at low pressures and temperatures (<1 atmosphere,approximately 200° C.). A typical bonding cycle for such a materialtakes place in a bonding tool where the glass and Si wafers are held inalignment but separated by a small gap to allow a vacuum to be createdbetween the wafer and the handler before the two are brought intocontact. The wafers are heated to the desired bonding temperature whilethey are pressed together. Bonding cycles are typically on the order of3 to 5 minutes. For higher temperature applications (e.g. approximately300° C. to approximately 350° C.) the adhesive choices are fewer, andinclude BCB and polyimide-based materials such as HD MicrosystemsHD3007. These are generally much less viscous once cured, and may bebonded at higher pressures and temperatures (>1 atmosphere,approximately 300° C. to approximately 350° C.). The adhesive chosen maybe spin applied at approximately 500 to approximately 3000 rpm,soft-baked at between approximately 80° C. and approximately 120° C. andthen cured at between approximately 300° C. and approximately 350° C.for up to an hour in nitrogen. Bonding cycles may be on the order ofapproximately 20 to approximately 40 minutes for these materials.

Laser debonding to release the glass handler at the ablation laterinterface may be performed using any one of a number of UV laser sourcesincluding excimer lasers operating at 308 nm (e.g. XeCl) or 351 nm (e.g.XeF) as well as diode-pumped (tripled) YAG laser operating at 355 nm ordiode-pumped (quadrupled) YAG laser operating at 266 nm. Excimer lasersmay be more expensive, may require more maintenance/support systems(e.g. toxic gas containment) and may have generally have very largeoutput powers at low repetition rates (e.g. hundreds of Watts output atseveral hundred Hz repetition). UV ablation thresholds in the materialsspecified here may require 100-150 milliJoules per square cm (mJ/sq·cm)to effect release. Due to their large output powers, excimer lasers cansupply this energy in a relatively large area beam having dimensions onthe order of tens of mm² area (e.g. 0.5 mm×50 mm line beam shape). Dueto their large output power and relatively low repetition rate, a laserdebonding tool which employs an excimer laser may consist of a movablex-y stage with a fixed beam. Stage movement may be on the order of 10 to50 mm per second. The wafer pair to be debonded may be placed on thestage, and scanned back and forth until the entire surface had beenirradiated.

An alternative laser debonding system may be created using a lessexpensive, more robust and lower power solid-state pumped tripled YAGlaser at 355 nm by rapidly scanning a small spot beam across the wafersurface. The 355 nm wavelength laser may compare favorably to thequadrupled YAG laser at 266 nm for two reasons: 1) Output powers at 355nm are typically 2 to 3 times larger than at 266 nm for the same sizeddiode laser pump power, and 2) many common handler wafer glasses (e.g.Schott Borofloat 33) are ˜90% or more transmissive at 355 nm but only˜15% transmissive at 266 nm. Since 80% of the power is absorbed in theglass at 266 nm, starting laser powers may be ˜6× higher to achieve thesame ablation fluence at the release interface, and there is risk ofthermal shock in the glass handler itself.

An exemplary 355 nm scanning laser debonding system may include thefollowing: 1) a Q-switched tripled YAG laser with an output power of 5to 10 Watts at 355 nm, with a repetition rate between 50 and 100 kHz,and pulsewidth of between 10 and 20 ns. The output beam of this lasermay be expanded and directed into a commercial 2-axis scanner,comprising mirrors mounted to x and y galvanometer scan motors. Thescanner may be mounted a fixed distance above a fixed wafer stage, wherethe distance would range from 20 cm to 100 cm depending on the workingarea of the wafer to be released. A distance of 50 to 100 cm mayeffectively achieve a moving spot speed on the order of 10meters/second. An F-theta lens may be mounted at the downward facingoutput of the scanner, and the beam may be focused to spot size on theorder of 100 to 500 microns. For a 6 watt output power laser at 355 nm,at 50 kHz repetition and 12 ns pulsewidth, a scanner to wafer distanceof 80 cm operating at a raster speed of 10 m/s, the optimal spot sizemay be on the order of 200 microns, and the required ˜100 mJ/sq·cmablation fluence may be delivered to the entire wafer surface twice in˜30 seconds (for example, using overlapping rows). The use ofoverlapping rows where the overlap step distance equals half the spotdiameter (e.g., 100 microns) may ensure that no part of the wafer ismissed due to gaps between scanned rows, and that all parts of theinterface see the same total fluence.

FIG. 1 is a flow chart illustrating an approach for performing handlerwafer bonding and debonding in accordance with exemplary embodiments ofthe present invention. First the release layer and the adhesive layermay be applied. According to one exemplary approach, the release layermay be applied to the handler (Step S11) while the adhesive layer may beapplied to the device wafer (Step S12). However, according to otherexemplary approaches, the release layer may be applied to the handlerand then the adhesive layer may be applied to the release layer.

The release layer is always interposed between the glass and theadhesive. Thereafter, the device wafer may be bonded to the handler(Step S13) such that the release layer and the adhesive layer areprovided between the device wafer and the handler. The bonding mayinclude a physical bringing together of the device wafer and the handlerunder controlled heat and pressure in a vacuum environment such asoffered in any one of a number of commercial bonding tools.

After the device wafer has been successfully bonded to the handler,desired processing may be performed (Step S14). Processing may includesuch process steps as patterning, etching, thinning, etc. until thedevice wafer has achieved its desired state. Thereafter, the circuitryof the device wafer may be inspected (Step S15). Inspection of thedevice circuitry may be performed to ensure that the device wafer hasbeen properly processed. Inspection may be optically performed, forexample, using a high quality microscope or other imaging modality.Optical inspection may be performed though the handler, which, asdescribed above, may be transparent. Optical inspection of the devicecircuitry may also be performed through the release and adhesive layersas each of these layers may be transparent as well.

Optical inspection may be performed after all processing has beencompleted and/or at any stage during the processing of the wafer.According to some exemplary embodiments of the present invention,optical inspection may be performed after one or more criticalprocessing steps that are likely to create defects. In the event thatoptical inspection results in a determination that a defect is presentin the device wafer, the device wafer may be rejected on the spot andsubsequent processing may be canceled. Because the device wafer may beoptically inspected through the handler, removal of the device waferfrom the handler is not required to perform testing and accordingly,defects may be detected at an earlier stage in processing than wouldotherwise be possible. Additionally, waiting until the entire 3D stackhas been assembled before performing testing may result in the rejectionof the entire 3D stack thereby substantially reducing yield and addingsubstantially to the cost of manufacture. Moreover, seeing the bondedinterface through the glass may be useful in that it may be verifiedthat processing has not generated small voids in the bonding adhesiveitself, which can lead to yield loss during thinning and vacuumprocessing. Because defects such as these may be known to exist at earlystages of processing, subsequent processing steps performed on the waferdefective may be avoided.

This opportunity for optically inspecting the device wafer may not bepresent in prior art approaches such as the 3M light-to-heat-conversion(LTHC) approach discussed above, where the LTHC layer is necessarilyopaque in order to be able to generate heat from the infrared laserlight exposure.

After inspection and any necessary repair has been performed to thedevice wafer, a laser ablation process may be performed to sever thedevice wafer from the handler (Step S16). Laser ablation may beperformed by exposing the release layer to UV laser light through thetransparent handler. Upon exposure to the UV laser light, the releaselayer may burn, break down or otherwise decompose. This stands incontrast to the 3M LTHC approach discussed above, where the LTHC layergenerates heat as a result of being exposed to the infrared laser lightand the heat in turn softens the adhesive layer to the point where thedevice wafer may be peeled from the handler. Thus, the release layeraccording to exemplary embodiments of the present invention comprises amaterial that is broken down under the exposure of the UV laser light.As the adhesive layer may remain hard during this process, the devicewafer, along with the adhesive layer, may be easily removed from thehandler. Where desired, the remainder of the adhesive layer may beremoved from the device wafer using various processing techniques.

Because the release layer burns away during the debonding, the debondingmay be substantially cleaner than conventional techniques such as the 3MLTHC approach discussed above.

After the laser ablation has resulted in the severing of the devicewafer from the handler, the device wafer may be easily removed from thehandler, for example, by simply pulling the handler away, and the devicewafer may be cleaned to remove the adhesive (Step S17).

FIG. 2 is a schematic diagram illustrating bonding and debonding of adevice wafer to a handler in accordance with exemplary embodiments ofthe present invention. The device wafer 21 may be a silicon wafer thatis to be processed, for example, to be added to a 3D stack such as alayer in a 3D IC or an IC to be included in a 3D package. The devicewafer 21 may be processed prior to bonding, however, prior to bondingthe device wafer 21 may be a full-thickness wafer. The device wafer 21may be bonded to the handler to provide structural support theretoduring subsequent processing which may include a thinning of the devicewafer 21 to the point where it may no longer poses the structuralintegrity necessary to withstand certain processing steps that may haveto be performed. The device wafer need not comprise silicon and mayinstead comprise an alternative semiconductor material. The device wafer21 may originate as a full-thickness wafer and may subsequently bethinned down to a size of between approximately 200 um and 20 um.

The handler 22 may be a transparent substrate and may comprise, forexample, Borofloat glass. The handler may be sufficiently thick toprovide structural integrity to the device wafer 21 bonded thereto. Forexample, the handler may be approximately 650 μm thick.

As described above, the adhesive layer 23 and the release layer 24 maybe provided between the device wafer 21 and the handler 22. According toone exemplary embodiment of the present invention, the release layer 24is disposed directly upon the handler 22. The release layer 24 maycomprise a material that is highly specialized to absorb strongly nearthe UV wavelength of laser light used during laser ablation. Asexemplary embodiments of the present invention may employ a UV laser,for example, at or near the wavelength 355 nm, the release layer 24 maycomprise a material highly absorbent of UV light, and in particular,light having a 355 nm wavelength. The release layer 24 may itselfcomprise an adhesive, but at least for reasons discussed below, therelease layer 24 may be an entirely distinct layer from the adhesivelayer 23.

The release layer 24 may comprise, for example, HD3007, which is apolyimide-based adhesive which may be spin applied and cured at 350° C.The release layer may be approximately 6 μm thick. The thermoplasticnature of HD3007 and similar materials may permit the release layer 24material to be applied in a liquid state and to flow to fill the surfaceof the handler 22 during application of the release layer 24. Thismaterial may be strong enough to withstand commonly used processingtechniques that may subsequently be performed on the device wafer 21while bonded to the handler 22 without the release layer 24 prematurelybreaking down. Such processes may include wafer grinding, application ofheat in excess of 260° C., PECVD, CMP, metal sputtering at 200° C., seedmetal wet etch, resist strip, and polymer curing at 320° C.

Additionally, while HD3007 may stand up to processing steps such asthose described above, it may also strongly absorb UV light and may beeasily ablated by radiation from a 308 nm excimer laser.

An example of a more advantageous UV release layer which is not itselfan adhesive, but rather an optically planarizing material used as anunderlayer in photolithography, is Shin Etsu ODL-38. Very thin layers ofthis material on the order of 1000 Å may be spin applied to glasshandlers and cured at 350° C. in nitrogen. This material absorbs verystrongly at UV wavelengths below ˜360 nm and decomposes rapidly, andthus is an excellent release layer for use at the 355 nm laserwavelength.

Regardless of the material used, the release layer 24 may comprise amaterial that can be laser ablated at the UV wavelength of choice. Therelease layer 24 may be generated, for example, by spin coating orspraying the release layer material, for example, onto the handler, andthen curing the material using heat (e.g. 350° C.) and/or UV light.Curing of the release layer material may either be performed prior tobonding of the handler 22 to the device wafer 21 or at the same time.

The adhesive layer 23 may be created by applying an adhesive material toeither the device wafer 21 or to the release layer 24. The adhesivelayer 23 may comprise a distinct material from that which is used as therelease layer 24, and in particular, the adhesive layer 23 may be anadhesive that does not strongly absorb the light of the wavelength thatis used to ablate the release layer 24. While any number of suitableadhesives may be used for this layer, one example of a suitable adhesiveis TOK A0206. The adhesive layer may be created, for example, byapplying the adhesive material to the device wafer 21. The adhesivelayer 23 may be cured using heat (e.g. 220° C.).

According to one exemplary embodiment of the present invention, therelease layer 24 may be cured prior to performing bonding. In this way,potential adverse interaction between the release layer 24 material andthe adhesive layer 23 material may be minimized. Bonding may beperformed in a bonder, for example, a Suss bonder using approximately500 mbar of applied force in a temperature of 220° C. (the curingtemperature of the adhesive layer 23 material). In bonding, the devicewafer 21 may be bonded, by the adhesive layer 23, to the handler 22having the release layer 24 attached thereto.

Thereafter, processing, testing, and repair may be performed, forexample, as described in detail above. Testing and inspection may befacilitated by the use of a transparent handler such as one made ofBorofloat glass.

When the processing, testing and repair is complete, and it is time todebond the device wafer 21 from the handler 22, a laser 25 may be usedto irradiate the release layer 24. As discussed above, the laser may bea 308 nm excimer laser or a 355 nm DPSS laser, for example, one createdby frequency tripling a diode-laser at 1064 nm. According to oneexemplary embodiment of the present invention the laser 25 may be aHIPPO 355QW laser with a wavelength of 355 nm, a power of 5 W at 50 kHz,a repetition rate of 15-300 kHz, and a pulse width of less than 12 ns at50 kHz. However, other UV lasers may be used such as a HIPPO 266QWhaving a 266 nm wavelength.

The release layer 24 may be irradiated though the handler 22, which maybe transparent, at least to the wavelength of the laser 25 used. Thelaser 25 may produce a spot beam that is scanned across the surface ofthe handler 22, for example, in a raster pattern, or the laser 25 mayproduce a fan beam that is swept once or multiple times across thehandler 22. Directing of the light radiated from the laser 25 may behandled by the use of a scanner and lens 26, which may be, for example,an F-Theta scan lens having an 810 mm fl. FIG. 3 is a schematic diagramillustrating pattern of applying the laser light to a top surface 31 ofthe handler 22 in accordance with exemplary embodiments of the presentinvention. As seen in FIG. 3A, the laser light may be directed acrossthe top surface 31 of the handler 22 as a spot beam drawn to lines 32which move along an x-axis direction of the top surface 31 of thehandler 22 with each successive line 32 being drawn lower in the y-axisdirection. Alternatively, as seen in FIG. 3B, the laser light may bedirected in a serpentine pattern 33.

As the UV wavelength of the laser 25 used may contain relatively highenergy, the light may efficiently ablate the release layer 24. Onceablated, the device wafer 21 may be freely removed from the handlerlayer 22. Thereafter, a solvent or cleaning chemical may be used toremove any remaining elements of the adhesive layer 23 and/or releaselayer 24 that may remain on the device wafer 21. The debonded andcleaned device wafer 21 may then be further processed, diced and appliedto a 3D stack and/or joined to a package or another 3D element.

FIG. 4 is a schematic diagram illustrating an apparatus for performinglaser debonding in accordance with exemplary embodiments of the presentinvention. According to some exemplary embodiments of the presentinvention, such as is shown here in FIG. 4, the bonded handler anddevice wafer 41 may remain stationary, for example, on a stage.According to other exemplary embodiments, the stage may be movable. Thelaser 42 may provide a beam that may then be sent into a beam expander45 to provide the desired beam size. The beam may then enter a scanner46 where the beam can be directed along the x and y axes. One or morecontrol units 43 may affect control of the laser 42, beam expander 45and the scanner 46. Where the stage upon which the bonded handler andwafer 41 are held is movable, the controller 43 may control the movementof the stage as well. In such a case the scanner 46 may be omitted. Acomputer system 44 may be preprogrammed with the manner of control andthese instructions may be executed though the one or more control units43. A scan lens 47 may adjust the beam so as to strike the bondedhandler and device wafer 41 with the desired spot characteristics.

Exemplary embodiments described herein are illustrative, and manyvariations can be introduced without departing from the spirit of thedisclosure or from the scope of the appended claims. For example,elements and/or features of different exemplary embodiments may becombined with each other and/or substituted for each other within thescope of this disclosure and appended claims.

What is claimed is:
 1. A bonded semiconductor wafer, comprising: atransparent handler; a device wafer bonded to the transparent handler; arelease layer, vulnerable to ablation by ultraviolet laser radiation andtransparent to visible light, provided directly on the transparenthandler, between the transparent handler and the device wafer; and anadhesive layer interposed between the transparent handler and the devicewafer.
 2. The bonded semiconductor wafer of claim 1, wherein thetransparent handler comprises Borofloat glass.
 3. The bondedsemiconductor wafer of claim 1, wherein the transparent handler issubstantially transparent to ultraviolet and visible light.
 4. Thebonded semiconductor wafer of claim 1, wherein the transparent handleris approximately 650 μm thick.
 5. The bonded semiconductor wafer ofclaim 1, wherein the device wafer includes integrated circuit elements.6. The bonded semiconductor wafer of claim 1, wherein the device waferincludes one or more through-silicon via (TSV).
 7. The bondedsemiconductor wafer of claim 1, wherein the device wafer is a layer fora 3D integrated circuit or 3D package.
 8. The bonded semiconductor waferof claim 1, wherein the adhesive layer is TOK A0206.
 9. The bondedsemiconductor wafer of claim 1, wherein the release layer comprises anadhesive.
 10. The bonded semiconductor wafer of claim 1, wherein therelease layer comprises HD3007.
 11. The bonded semiconductor wafer ofclaim 1, wherein the release layer comprises cyclohexanone.
 12. Thebonded semiconductor wafer of claim 1, wherein the release layer isapproximately 6 μm thick.
 13. The bonded semiconductor wafer of claim 1,wherein the release layer strongly absorbs a frequency of light radiatedfrom an ablating laser.
 14. The bonded semiconductor wafer of claim 13,wherein the frequency of light radiated from the ablating laser isapproximately 350 to 360 nm.
 15. The bonded semiconductor wafer of claim13, wherein the power of light radiated from the ablating laser isapproximately 5 to 30 Watts.
 16. The bonded semiconductor wafer of claim1, wherein the release layer is vulnerable to ablation by ultravioletlaser radiation.
 17. The bonded semiconductor wafer of claim 16, whereinthe release layer is vulnerable to ablation by ultraviolet laserradiation of a power within the range of approximately 5 to 30 Watts.18. The bonded semiconductor wafer of claim 1, wherein the transparenthandler, the adhesive layer, and the release layer are configured topermit inspection of the device wafer therethrough.
 19. A bondedsemiconductor structure, comprising: a transparent substrate; asemiconductor wafer bonded to the transparent substrate; a firstadhesive layer interposed between the transparent substrate and thesemiconductor substrate; and a second adhesive layer, vulnerable todestruction by ultraviolet laser radiation and transparent to visiblelight, provided directly on the transparent substrate and between thesemiconductor wafer and the transparent substrate.
 20. The bondedsemiconductor structure of claim 19, wherein the second adhesive layercomprises HD3007 or cyclohexanone.